ParabolaHard

Question

The equation of the common tangent to the curves y2 = 8x and yx = - 1 is

Options

A.3y = 9x + 2
B.y = 2x +1
C.2y = x + 8
D.y = x + 2

Solution

Tangent to the curve y2 = 8x is y = mx + , So, it must satisfy xy = - 1
⇒    
⇒    
Since, It has equal roots.
∴     D = 0
⇒     4m = 0 ⇒ m3 = 1 ⇒ m = 1

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